In the electric discharge cutting of workpieces, the prime goal is to automate the cutting process or processes insofar as possible. The manual intervention of an operator and, in particular, the need for his presence for control purposes are to be avoided as far as possible. In the traditional wire discharge machines, this has had the result that, after programming, the necessary cuts can be effected substantially entirely automatically without the presence of the operator. The four most widely used types of cuts in electroerosive machining with the use of a wire are explained below.
For the cutting of a die in a workpiece, a starting hole is customarily the first step performed in the workpiece. A shape is cut around the starting hole into the workpiece which is to be machined. For this purpose, a solid cut is first of all effected into the workpiece. In order to improve the surface tolerances of the die to be produced, finish cuts are made along the path of the solid cut. These finish cuts, of course, proceed substantially faster than the solid cut since much less material need be removed.
In order that the shaped piece which has been cut out around the starting hole does not simply drop out of the workpiece and damage parts of the wire discharge machine, a short distance, the so-called parting-cut path, is initially left uncut after the solid cut. This parting-cut path is the final attachment between the workpiece and the shaped piece which has been cut out. When an operator is present, the parting cut is finally effected along the parting-cut path. The drop-out piece produced upon the cutting out of the workpiece can in this way be removed in controlled manner by the operator. Finally, after the parting cut, finish cuts are effected along the parting-cut path in order to improve the surface quality of the die.
In the case of a punch, substantially the same shaped pieces are produced as in the case of a die. Differing from the production of a die however, the starting point for the cutting, i.e. the drilling of the starting hole, is located outside the punch, i.e. in the workpiece which still remains after the cutting. Nor is this surprising since, upon the production of a punch, the important factor is no longer the workpiece. It can therefore be to a certain extent destroyed by the starting hole.
The cutting sequence discussed above with respect to the die remains substantially the same upon the production of a punch. However, as soon as the solid cut and all finishing cuts along the solid cut path have been completed in the case of the production of a punch, the operator must so secure the punch in the workpiece that it remains therein. For this purpose, he can use different means, for instance magnets, adhesive parts, or else clamping between workpiece and shaped piece, in known manner.
Once the shaped piece--i.e. the punch--which has been almost completely cut out of the workpiece is fixed in place after the solid cut, the remaining parting cut and the following finishing cuts can be effected along the parting-cut path.
Differences in the production of dies and punches result from the fact that, in the case of the die, importance is placed on the inner surface of the cut workpiece while in the case of the punch, importance is placed on the outer surface of the workpiece. In both cases, the presence of the operator for the securing or removal of the shaped piece is required shortly before or during the carrying out of the corresponding parting cut.
For the sake of completeness, the two other customary types of cutting may also be mentioned: They are, on the one hand, the full-removal cut in which the material is eroded away within a contour without shaped pieces resulting. On the other hand, there is the so-called open contour, i.e. the machining of the outer side of a workpiece. With this type of cut, one proceeds substantially in exactly the same manner as upon the further machining of the aforementioned punch.
Until recently, the above explained presence of the operator was always necessary after a very specific sequence of cuts. Therefore, when certain cuts were completed and the operator was accordingly necessary but not present, this led to an uneconomic interruption of the entire machining process. This state of affairs is particularly disadvantageous upon the machining of several workpieces or upon the production of several shaped pieces in one workpiece. At the same time, up to now the operator was dependent on the wire discharge machine since, despite the best possible organization of the work, he nevertheless had to be present at a very specific moment, namely at the time of the parting cuts.